Digital television systems and receivers have proliferated in the past few years. Some examples include DIRECTV, DVB (Digital Video Broadcasting project) and ATSC (Advanced Television System Committee) type systems. Because of the considerable amount of data associated with video communication, compression has become an integral part of most modern digital video applications.
The Moving Pictures Experts Group has defined a standardized video compression method for video signals and pictures known as the MPEG (Moving Pictures Expert Group) image encoding standard, hereinafter referred to as the “MPEG standard”. The MPEG standard is comprised of a system encoding section (ISO/IEC 13818-1, 10 Jun. 1994) and a video encoding section (ISO/IEC 13818-2, 20 Jan. 1995). Data encoded to the MPEG standard is in the form of a packetized datastream which typically includes the data content of many program channels (e.g. content corresponding to cable television channels 1–125). The MPEG standard uses both intraframe and interframe coding techniques to obtain the desired compression. In intraframe coding of an image frame, a frame is divided into pixel blocks (termed macroblocks) and individual blocks are compressed using a discrete cosine transform (DCT). In interframe coding of an image frame, further data compression is achieved using Motion Compensation (MC) techniques to predictively encode image frame differences.
The three primary types of frames involved in MPEG image encoding are Intrafame-coded (I) frames, Predictively-coded (P) frames and Bi-directionally-predictively-coded (B) frames. I-frames provide random access points into a data stream (representing an image sequence) and an individual I-frame is decoded and reconstructed without the use of data from any other frame. P-frames are reconstructed using data from previous I or P-frames (anchor frames) using motion estimation techniques. B-frames are reconstructed using data from both previous and future I and P anchor frames and may involve processing frame data in a sequence that is different to the received frame sequence. Significant data compression may be achieved in this way since B-frames, for example, require only about 11% of the data required for an I-frame.
Digital television receivers, such as those compatible with DIRECTV, DVB, and ATSC requirements, may involve objectionably long program acquisition times following a User initiated channel change. The time between User selection of a new channel (and associated signal source) and the initial display of the new program on the selected channel may amount to several seconds, for example. This is due, at least in part, to the sequence of acquisition events required before a data stream may be captured, processed and displayed. In particular, a channel change and new program acquisition may require identification and use of a random entry point in a compressed data stream representing a program on the newly selected channel. Further, if the newly selected channel is located in a datastream being transmitted on a different transponder or RF channel, a channel change may necessitate repeating phase-lock and equalization operations. In addition, following such phase-lock and equalization operations, it is necessary to capture ancillary system and program specific information from within a received transport stream (TS). This system and program specific information is parsed, collated and assembled into usable form for use in identifying and assembling individual data packets to recover a program on the newly selected channel. The program specific information also contains program guide, conditional access, network information and identification and linking data enabling system tuning to a desired channel. Once the program specific information has been captured and assembled it is used to identify and capture individual data packets comprising a program being conveyed on the newly selected channel. The individual data packets comprising the program on the newly selected channel, are buffered to be compatible with MPEG compatible Video Buffering Verifier (VBV) requirements and a sequence-header and I-frame are identified in order to provide an appropriate entry point for subsequent processing and display.
A system according to the present invention reduces the delay involved in channel change and minimizes any associated User objectionable viewing interruption.